R gunn



"eh. 20. 1940. R GUNN Re. 21,361

APPARATUS FOR THE DETECTION OF DISPLACEMENTS 3 Sheets-Sheet 1 OriginalFiled Dec. 4, 1936 INVENTOR H055 (hum ATTORNEY Feb. 20, 1940. R. GUNNRe. 21,361

APPARATUS FOR THE DETECTION OF DISPLACEMENTS Original Filed Dec. 4, 19363 Sheets-Sheet 2 AIIIHIII III INVENTOR R055 (in/um BY 4 W A TTORNEY R.GUNN Feb. 20, 1940.

APPARATUS FOR THE DETECTION OF DISPLACEMENTS Original Filed Dec. 4, 19363 Sheets-Sheet I5 lOl INVENTOR Ross Gunn. W

ATTORNEY Reissued Feb. 20, 1940 UNITED STATES PATENT OFFICE Rosa Gunn,Washington, D. 0.

Original No. 2,155,419,

for reissue December 308,883

12 Claims.

(Granted dated April 25, 1939, Serial No. 114,111, December 4, 1936.Application 12, 1939, Serial No.

under the act of March 3. 1883, as

amended April 30, 1928; 370 O. G. 757) My invention relates to anapparatus tor detecting displacements and more particularly to anelectrical apparatus for the remote and substantially instantaneousdetection or measurement of mechanical displacements.

In carrying out my invention I employ a space discharge device whichincludes at least a cathode and a movable anode and provide meansresponsive to the displacement to be detected or measured for impartingmovement to the said anode. Any movement imparted to the anode resultsin a change in the average internal resistance between the anode andcathode with at tendant change in the space current through the spacedischarge device. By connecting the space discharge device in a propercircuit and providing suitable indicating or recording means, adisplacement c! any desired character or magnitude may be detected ormeasured. Various types of novel space discharge devices and circuitsmay be advantageously employed in carryin my invention into effect allof which will be pointed out more in detail hereinafter.

The apparatus of my invention is capable oi detecting or measuring highfrequency periodic or non-periodic mechanical displacements. whosevalues closely approximate the wave length of red light and by theemployment of suitable auxiliary means is readily adaptable to detectingor measuring displacements even to as great a value as a foot. Becauseoi. its simplicity, ruggedness, practicability and extreme sensitivity,my apparatus has a wide field at application. As illustrative or itsmany uses it may be employed for detecting or measuring mechanical orelastic vibrations such as occur in bridges, buildings, variousmachinery and other structures; for detecting or recording earthquakes,either natural or such as are produced as incidental to geo-physicalexploration; for detecting or measuring elastic defamation such, torexample. as would occur in a ship's structureor a propeller shaft; fordetecting or measuring angular displacements; and for detecting ormeasuring instantaneous liquid or gaseous pressures. Many other useswill readily occur to those skilled in the art.

With the foregoing preliminary discussion in view, it is an object of myinvention to provide a simple, rugged and eflective electrical apparatusfor detecting or measuring periodic or non-periodic mechanicaldisplacements of either large or small magnitude.

It is another obiect of my invention to provide an electrical apparatusfor detecting or measuring mechanical displacements wherein any changein the value of an electro-motive force incorporated in a balancedelectrical circuit of the apparatus or any change in the electronemissivity of a cathode oi a space discharge device incorporated in alike circuit and iorming part of the apparatus will not aiiect anyindication of the indicating means.

It is another and further object my invention to provide an electricalapparatus tor detecting or measuring angular displacements.

It is another and still further object 01 my invention to provide newand novel space discharge devices for incorporation in my detecting ormeasuring apparatus but which, however. are .susceptible oi. beingadvantageously used in other environments.

Other objects and many of the attendant advantages of this inventionwill be readily appreciated as the same becomes better understood byreference to the following detailed description when considered inconnection with the accompanying drawings, wherein:

Fig. 1 discloses one embodiment 01 my invention;

Fig. 2 discloses an alternative embodiment of my invention employing adifferent space discharge device and circuit arrangement;

Fig. 3 depicts a further modification of my invention differing overthat of Fig. 2 principally in the employment of a grid circuit;

Fig. 4 shows another form that my invention may take and wherein adiflerential galvanometer is employed;

Fig. 5 depicts a still further embodiment of my invention which isespecially designed for detecting or measuring angular displacements;

Fig. 6 is a sectional view taken on the line 8-0. Fig. 5;

Fig. 7 shows another modification 01 my appsratus employing two cathodesin the space discharge device thereof and an amplifier for amplifyingany voltage diflerential of the bridge circult;

Figs. 8 and 9 represent different embodiments of my invention whereinthe displacement of the movable electrode or electrodes of the spacedischarge device is controlled by suitable external magnetic means; and

Fig. 10 depicts a modification 01 my invention suitable tor thedetection or measurement of fluid pressure.

Before proceeding with a detailed description of the various embodiments01 my invention it is deemed advisable at this point in the interest ofclarity and in order to avoid needless repetition in the subsequentdescription to make certain general remarks concerning the spacedischarge devices and circuits employed in my apparatus. As pointed outhereinbefore, each space discharge device includes at least one cathodewhich serves as a source of electrons. A cursory examination of thedrawings will show that all cathodes have been depicted therein as ofthe thermionic type, the heating thereof to insure electron emissionbeing accomplished either directly or indirectly by a suitable source ofelectro-motive force. I wish to emphasize in this connection, however,that I do not desire to be restricted to this type of cathode sincecathodes which emit electrons due to bombardment by rapidly moving ions,electrons, or metastable atoms and are said to be secondarily emissive,or photo-electric cathodes, or cold or non-thermionic cathodes whichspontaneously emit electrons due to-treatment thereof by a radioactivesubstance, all will serve the purpose of my invention equally well. Asfor the thermionic cathode, it may be fabricated of a pure metal, beoxide-coated, be of a metal provided with an adsorbed monatomic film ofone of the electro-positive metals or be of any other type known to theart. The envelopes of my space discharge devices which are fashionedfrom any of the materials known to the prior art and serve to enclosethe electrodes may be evacuated to produce a high vacuum and thus insurea substantially pure electron discharge or may alternatively be providedwith a suitable filling of a gas or vapor, gases or vapors, or mixturesof gases and vapors at a selected pressure or pressures to insure thedesired operating characteristics.

Many of the circuits employed in various embodiments of my inventiontake the form of a Wheatstone bridge in which three electrodes oi aspace discharge device are connected to form two branches thereof, theremaining two branches being formed by two variable resistances whichserve to eflect a balancing of the bridge circuit prior to any detectingoperation. Means responsive to the displacement to be detected ormeasured serve to impart movement to at least one of the said threeelectrodes to cause simultaneously thereamong a decrease in electricalresistance between the first and second electrodes and an increase inelectrical resistance between the first and third electrodes, thuscausing an unbalancing of the bridge circuit which is indicated by asuitable indicating or recording device. It is, of course, apparent thatthe indicating device may be suitably calibrated to indicate not onlythe magnitude of the displacement but also its direction.

The basic principle underlying my invention may be best appreciated byconsidering the embodiment disclosed in Fig. 1 of the drawings. There isshown depicted in this fi ure an envelope I of a space discharge devicewhich includes as part thereof a flexible bellows-like metallic or glassextension 2 to the end of which is rigidly secured the anode 3 by meansof the lead-in wire 4. A cathode I, which may be of a thermionic type,is heated to an electron emissive temperature by the source ofelectro-motive force I. The plate circuit of the space discharge deviceincludes the source of electro-motive force I and an indicating device 8which may be a milliammeter. The force, pressure or displacement to bedetected is represented schematically by the arrow 9/ A small spring andanvil III are arranged to return the extension 2 of the space dischargedevice to its initial and desired position with a given plate potentialthe space current density varies in a non-linear manner with theelectrode spacing and increases rapidly as the spacing between the anodeand cathode structures is reduced. This fact was first established byChild andis known as Child's law. Thus, the

average internal resistance between the anode 3 and cathode 5 is adefinite and reproducible function of the spacing between theseelectrodes, which spacing is controlled by displacing the end of theflexible extension 2 by a force or pressure 9. It is therefore evidentthat any change in spacing between the electrodes 3 and 5 will result ina. changein space current, the indicating device 8 reading more or lessdepending upon whether the spacing between the electrodes is decreasedor increased. Hence, any departure from a predetermined and initialreading or reference point of the milliammeter serves to detect adisplacement, the magnitude of which is easily ascertainable by suitablecalibration of 1 the milliammeter or indicating means 8.

While the apparatus of Fig. l is an entirely operative and usefulstructure it does, nevertheless, possess certain inherent disadvantages.If. for example, the emissivity of the cathode 5 is in any mannerimpaired or the value of the electromotive force of either sources 5 orI changes, this will be evidenced by first order changes in the platecurrent indicated by the milliammeter 8. If, then, the indicating meanshas been previously calibrated for a fixed electron emissivity and fixedvalues of electro-motive forces, it is evident that the indicating means8 will now give inaccurate and false readings because of a changedreference point. In order to minimize any such difllculty as might beencountered in using the apparatus of Fig. 1, I provide different tubestructures and circuit arrangements as will be pointed out hereinafter.

In Fig. 2 oi the drawings there is shown a space discharge device andcircuit arrangement which minimize the difliculties that may beencountered with the apparatus of Fig. 1. In this figure ll denotes theenvelope of the space discharge device which like that of Fig. 1 has atone end thereof a flexible metallic or glass bellowslike extension I! towhich are secured and insulated from each other the two anodes l3 and I4supported by their respective lead-in wires I 5, I B. The cathode I?which may be of a thermionic type is heated to an electron emissivetemperature by the battery iii. The insulated lead-in wires II and itare connected in a bridge circuit which includes the two balancingresistances l9 and ill. It is thus seen that the bridge circuit includesfour arms or branches, two of which are constituted by the resistancesbetween the anode II, cathode l1, and anode ll, cathode II with theresistances i9 and 20 heretofore mentioned forming the remaining twobranches. The indicating device II which may be a milliammeter is placedacross one diagonal of the bridge and the plate potential or source ofelectro-motive force 22 connected across the remaining diagonal. A smallspring and anvil 23 again serve to return the extension or projection I!of the space discharge device to its initial and desired position ofrest upon the removal of any actuating force. I! now the end of theextension of projection I2 is displaced in any manner, such as forexample by the indicated micrometer 24, the anode 12 will move towardthe cathode l1 while simultaneously the anode M will move away from thecathode. this movement of the electrodes occurring due to the fact thatthe anodes l3 and I4 are rigidly secured to the end of the projection orextension l2 by means of the lead-in wires 15 and 16. The formerelectrode movement tends to decrease the internal resistance between theanode l3 and cathode l1 and the latter has a tendency to increase theresistance between the anode l4 and cathode I1. It, then, the bridge bebalanced by a suitable adjustment of the variable resistances I9 and 2|)prior to the application of a force by the micrometer 24, the bridgewill now be unbalanced in both its arms by the displacement of themicrometer. It is at once evident that any unbalanclng of the bridgecircuit will be indicated by the milliammeter 2| and that the directionof the indication of the mlliiammeter 2| will indicate the direction ofthe displacement. The apparatus of Fig. 2 possesses important advantagesover that disclosed in Fig. 1. For example, if the emission of thecathode I1 is in any manner impaired or if the values 01' theelectro-motive forces IB and 22 change, these changes or variations inemissivity and voltage will aflect the plate circuits in the bridgeequally and to the first order at least. These variations or changes,however, will not be indicated by the milliammeter 2| provided thebridge is balanced as indicated in Fig. 2 01 the drawings. Hence, theelectrical balance or zero reference point will remain fixed undervarying conditions of plate voltage and emissivity. This is a distinctadvantage and improvement over the apparatus of Fig. 1 in that anycorrection to the meter reading can now be easily made when based upon afixed reference point; whereas corrections to the meter in the apparatusof Fig. 1 are extremely diflicult because of its uncertain reierencepoint occasioned by any change in emissivity or voltage. It is thusclear that the apparatus of Fig. 2 provides a very rugged andpracticable structure for indicating or measuring displacements.

The apparatus shown in Fig. 3 is a variation of that shown in Fig. 2. Inthis figure the envelope 25 of the space discharge device is provided atone end thereof with a flexible metal seal 26 sealed to it in any mannerknown to the prior art, the said seal 28 having secured thereto thetubular metallic member 21 supporting the anode leads 28 and 29. Theanode lead 28, as shown, supports the anode 30 and is hermeticallysealed to and insulated from the tubular member 21 by means of theinsulating plug 3|. The metallic tubular member 21 besides serving toimpart movement to the anodes 20 and 22 serves also as a currentconductor. The cathode 23, which may be of a thermionic type, is heatedto an electron emissive temperature by the battery 34 and is surroundedby a grid which is connected to a suitable source of biasing voltage 38.The space discharge device 25 as in the preceding figure is connected ina bridge circuit to form two branches thereof, the remaining twobranches being constituted by the variable resistances 31 and 38. Anyconvenient source of electro-motive force 29 serves to supply thecurrent for energizing the bridge circuit. The tubular member 21 withthe anodes 30 and 32 rigidly secured thereto is moved by any means suchas the indicated micrometer 40. An osclllographic element 4! is shown inthe bridge circuit to emphasize the fact that periodic or rapiddisplacements of the small projecting tube may be indicated and recordedby photographic or other methods. The essential difference 01 theapparatus of Fig. 3 over that of Fig. 2 resides in the employment of agrid structure 35 and a biasing battery 36. This arrangement can be madesomewhat more sensitive than that of Fig. 2 and balancing of the bridgeis somewhat more convenient. The apparatus of Fig. 3, however, alsoemploys the fundamental principle of a change in plate resistanceattending the simultaneous movement of the anodes 30 and 32 as a resultof the application of a pressure or force to the tubular member 21.

Fig. 4 shows another modification of my apparatus wherein 42 denotes theenvelope enclosing the anodes 43, 44 and the thermionic cathode 45 whichis heated to an electron emissive temperature by the battery 48. Atubular member 41 supports the anodes 43 and 44 for movement within theenvelope and is identical in construction and mounting with that shownin Fig. 3 of the drawings. It is to be clearly understood that the spacedischarge device of Fig. 4 is identical in construction and operationwith that of Fig. 3 except that the grid has been omitted. Adiflerential galvanometer 48 with an appropriate balancing resistance 49is connected in the plate or bridge circuit of the space dischargedevice, a source of electro-motive force 50 serving to energize thecircuit. The windings 5| and 52 of the differential galvanometer are,01' course, connected so that they annul each other and if the currentincreases in one coil and decreases in the other, the deflection will beincreased due to both causes. The balancing resistance 49 connectedacross the coil 5| permits the employment of the differentialgalvanometer as a null instrument. Again, a spring and anvil areschematically represented at 53 to return the tubular member 41 to itsinitial and desired position of rest upon the removal of any actuatingforce. Anvils I4 and and a test object 56 suggest one use of theapparatus which is applicable to the modifications previously describedand to be described hereinafter. Thus, for example, if the test object56 is a standard test piece and is introduced between the anvils 54 and55 as shown the bridge may be balanced so that the galvanometer 48 willread some predetermined value. Then as object 56 is removed andcomparison objects are introduced in place thereof, the galvanometer orindicator 48 will read more or less than the value established for thestandard test piece, thus showing that the object under test is greateror less in diameter than the standard. The galvanometer 48 is readilycalibrated and standardized with the result that the exact amount ofdeparture of any test piece from that of the standard can be easily andquickly determined.

Figs. 5 and 6 illustrate a still further modification of my apparatuswhich is especially designed for indicating or measuring angulardisplacements. In this embodiment E1 designates the grid structuresurrounding the cathode 58 and as shown consists of a. plurality ofconductors i! which are arranged more or less parallel to the electronemissive cathode. The anode or plate structures 50 and BI are also eachmade of plurality oi conductors which are parallel to those u of thegrid and substantially parallel to the oathode and are so arranged thatwhen the conductors of the anode 99 (see Fig. 6) are behind the gridconductors and thus substantially fully shielded from the cathode, theconductors of the anode 9| are substantially fully exposed to thecathode. The envelope of the space discharge device includes aninsulating portion 92 to which is sealed a metallic portion 63 having apart thereof terminating at 64 which is flexible and to which twistingor torsional movements may be imparted. Rigidly secured to the part orextension 64 is a tubular metallic member 95 in which the lead-in wiresof the anodes 69 and BI are insulatingly supported and hermeticallysealed by the insulating plug 69. It is evident that any angularmovement of the extension 64 will result in rotary or angular movementof the anodes 99 and BI. A suitable source of electro-motive force 91serves to bias the grid while the remaining electrodes of the spacedischarge device are connected in a bridge circuit which includes thevariable resistances 68 and 69 and the voltage source I9 for energizingthe same. As in the previous embodiments of my invention a suitableindicating device II is provided for detecting any differential voltagein the bridge circuit. The manner of operation of the apparatus in Fig.5 is believed to be clear. Thus if any torsional movement is imparted tothe flexible extension 64 by any means whatsoever rotary movement of theanodes 69 and GI will result. Assuming that the initial positions of theanodes 99 and BI are shown in Fig. 6 if the movement is in the directionindicated by the arrow the conductors of the anode 69 will be exposedmore to the cath ode 58 while simultaneously the conductors of the anodeBI will be moved progressively from their exposed positions to thecathode to positions where they are shielded by the grid conductors. Ifthe bridge be balanced prior to the initiation of any movement it isclear that the angular displacement of the anode 69 will result in anincreased current flow thereto while the current to the anode BI isdecreased. Since movement of the anodes causes a variation in the tuberesistances with attendant variation of currents in the bridge circuitit is evident that the bridge is now unbalanced and any differentialvoltage thus caused is indicated by the indicating device II. In thismanner it is possible to indicate or meas-- ure angular displacements.

In the modification of Fig. 7, 12 indicates the envelope of the spacedischarge device to which is sealed the flexible metallic cap I3 formovably mounting the anode 14. The anode as shown is interposed betweentwo cathodes I5 and 16 of the indirectly heated type which are heated toan electron emissive temperature by the resistance units 11 and I8energized by the battery 19. A small spring and anvil 99 serve to returnthe anode to its initial and desired position of rest, movement beingimparted to the anode, for example, by the test piece 9| which is showninterposed between the anvil 92 and micrometer 93. The space dischargedevice of Fig. 7 has certain advantages over those previously describedin that it is not necessary to insulate two moving lead-in wires for theanodes and as in the previous embodiments is connected in a bridgecircuit which includes the variable resistances 94 and 95 and a suitablesource of electro-motive force 95. The apparatus depicted in Fig. 7,however, difiers over those previously described in that anydifferential voltage produced in one diagonal of the bridge circuit isamplified, this being accomplished by connecting parts of the bridgecircuit as shown to grid 89 and an indirectly heatedcathode 91 of anamplifier tube 89. This amplifier tube in turn forms one branch of asecond or auxiliary bridge circuit, the remaining three branches ofwhich are constituted by the variable resistances 89, 99 and 9| andenergized by a suitable source of electro-motive force 92. This schemeinsures amplification of any differential voltage in one diagonal of thefirst bridge circuit which is indicated or recorded by any properindicating means such as, for example, an oscillograph 93. It is to beemphasized that this arrangement for amplifying any difierential voltagemay be employed in any other modification of my invention and that anyconvenient number of stages may be employed.

A further modification of my invention is shown in Fig. 8 in which theanodes 94 and 95 aremade of a magnetic material which can be magnetizedby induction or may be permanent magnets with poles as indicated. Theanodes are secured to relatively flexible lead-in wires 99 and 91, acathode 99, which may be of a thermionic type, being interposed betweenthe said anodes. The electrodes of the space discharge device areconnected in a bridge circuit to form two branches thereof, theremaining two branches being formed by the variable resistances 99 andI99 and energized by a suitable source of electromotlve force I9I. As inthe previous modifications an indicating device I92 serves to indicateor measure any displacement of the anodes 94 and 95 with respect to thecathode 99. The position or the anodes within the space discharge deviceis controlled by any suitable external magnetic means such as, forexample, a permanent magnet I93. The position or the magnet I93 iscontrolled by the displacement which it is desired to detect or measure,it being apparent that the magnet may be moved in a desired manner.Thus, Ior example, rotation of the magnet I93 about its axis of symmetrywill produce a displacement of the magnetic anodes within the tube insuch a way that angular displacements may be readily indicated on themilllammeter or indicating device I92.

Fig. 9 illustrates another form which my apparatus may take. In thisembodiment two thermionic cathodes are employed, one of which isdesignated in general by the numeral I94 and made in two portions I94and I94", the remaining cathode I95 being similarly constructed andconsisting of the parts I95 and I95". The cathodes I94 and I95 areheated to an electron emissive temperature by the respective sources ofelectro-motlve force I96 and I91. The anode is shown at I99 as amagnetized body and is interposed and mounted for rotation between thecathodes, The space discharge device as in the previous embodiments isconnected in a bridge circuit to form two branches thereof, the

remaining two branches of which are constituted by the variableresistances I99 and H9 which are energized by the source ofelectromotive force III. Any differential voltage in a diagonal of thebridge is indicated by a suitable indicating device H2. As in themodification of Fig. 8 the position of the anode I99 is controlled byany suitable external magnetic means such as, for example, the magnetH9, the position of the said anode with respect to a selected initialposition being indicated by the indicating device H2.

One important application of my apparatus is to the measurement ofinstantaneous fluid pressures such, for example, as the changes inpressure in the cylinders of a Diesel engine when it is in operation.Fluid pressures of any character may be conveniently indicated ormeasured by the apparatus shown in Fig. 10 of the drawings. In thisembodiment Ill designates a vessel of any suitable insulating materialapertured at points H and II 6 and transversely of which there extendtwo flexible partitions III, I I8 which may be of metal to thus provideupper and lower chambers I I9, I20 and an intermediate hermeticallysealed chamber I2I. Anodes I22 and I28 are electrically connected to andsupported by the respective diaphragms or partitions H1, H8, athermionic cathode I24 being interposed between the anodes forcooperation therewith. As in many of the preceding em.- bodiments theelectrodes within the hermetically sealed chamber I2I are connected toform two branches of a bridge circuit of which the remaining twobranches are constituted by the variable resistances I25 and I26. Anysuitable indicating device I21 serves to indicate any dilierentialvoltage in the bridge circuit which is energized by the source ofelectro-motive i'orce I28. The chambers H9 and I20 serve as receptaclesfor the fluid, the pressure of which is to control the displacements ofthe diaphragms I I1 and 8. It is evident that any pressure applied tothe diaphragm IlI will cause a displacement thereof thus decreasing thespacing between the anode I22 and the cathode I24 with attendantunbalancing of the bridge circuit as evidenced by an indication of theindicating means I21. The indication of the indicating means I21 will ofcourse be proportional to the displacement of the diaphragm Ill. Thediaphragm II! .which is electrically connected in the bridge circuitsand to the anode I23 is introduced for two reasons. It serves as a meansfor balancing out irregularities in emission of the cathode or anyvoltage variation in the sources of electro-motive force under balancedcircuit conditions but is primarily intended to correct for any changesin barometric pressure. As pointed out hereinbefore, it the diaphragm III is subjected to fluid pressure the displacement of the diaphragm willbe proportional to the pressure exerted upon it. It, for example, theapparatus is employed as a fuel gauge in aircraft, operations at highaltitudes will reduce the displacement oi. the diaphragm Ill and inorder for the indicating device I21 to read the proper pressure-head theanode I23 must be displaced a distance equal to the distance displacedby the anode I22 due to the increased altitude. To insure a displacementof the anode I23 and hence a correct and accurate reading of theindicating device I21 the diaphragm H8 is provided. It is clear that theapparatus of Fig. may be used to indicate differential pressure.

All the novel features of my space discharge devices are claimed in thisapplication, the teatures of novelty of my system or apparatus as awhole, however, being claimed in application Serial Number l14,1l2 filedconcurrently herewith.

The invention herein described and claimed may be used and/ormanufactured by or for the Government of the United States oi Americafor governmental purposes without the payment of any royalties thereonor therefor.

I claim:

1. A space discharge device comprising an envelope enclosing at leastthree electrodes, said electrodes including two independent andimmovably mounted cathodes and one movably mounted anode, the said threeelectrodes being mounted for simultaneous cooperation and being disposedto cause an increase in one anode cathode resistance simultaneously witha decrease in a like resistance, and means operable to impart movementto said anode to cause a change in spacing between said anode andcathodes.

2. A space discharge device comprising an envelope enclosing at leastthree electrodes, said electrodes including at least one immovablymounted cathode and at least one movably mounted anode, the said threeelectrodes being mounted for simultaneous cooperation and being disposedto cause an increase in one anode cathode resistance simultaneously witha decrease in a like resistance, and means operable to impart rotationalmovement to at least one 01. said three electrodes to causesimultaneously thereamong a decrease in electrical resistance betweenthe first and second electrode and an increase in electrical resistancebetween the first and third electrode.

3. A space discharge device comprising an envelope enclosing at leastthree electrodes, the said three electrodes being mounted forsimultaneous cooperation and being disposed to cause an increase inresistance between two electrodes simultaneously with a decrease in alike resistance, and means operable to impart rotational movement to atleast one of said three electrodes to cause simultaneously thereamong adecrease in electrical resistance between the first and secondelectrodes and an increase in electrical resistance between the firstand third electrodes.

4. A space discharge device comprising an envelope enclosing a cathode,grid and two anodes, the said electrodes being mounted for simultaneouscooperation and being disposed to cause an increase in one anode cathoderesistance simultaneously with a decrease in a like resistance, and

'means operable to impart rotational movement to said anodes.

5. A space discharge device comprising an envelope enclosing a cathode,grid and two anodes, the said grid and anodes each being formed of aplurality of longitudinally extending conductors with the gridsurrounding the cathode, the said electrodes being mounted forsimultaneous cooperation and being disposed to cause an increase in oneanode cathode resistance simultaneously with a decrease in a likeresistance, and means operable to impart rotational movement to saidanodes.

6. A space discharge device comprising an envelope enclosing a cathode,grid and two anodes, the said grid and anodes each being formed of aplurality of longitudinally extending conductors which are arranged suchthat when the conductors of one anode are substantially fully shieldedby the grid conductors from the cathode the conductors of the otheranode are substantially fully exposed to the cathode, and means operableto impart rotational movement to said anodes to thereby vary thepositions of the anode conductors with respect to the grid conductors.

7. A space discharge device comprising an envelope enclosing twoindependent spaced electron emlssive cathodes and an anode interposedtherebetween, the said three electrodes bing mounted for simultaneouscooperation and being disposed to cause an increase in one anode cathoderesistance simultaneously with a decrease in a like resistance, andmeans operable o mpart movemeat to said anode to cause simultaneously adecrease in spacing between the said anode and first cathode and anincrease in spacing between the said anode and the second cathode.

8. A space discharge device comprising an envelope including at each enda flexible metallic diaphragm, an anode electrically connected to andsupported by each diaphragm and a cathode interposed between saidanodes.

9. A space discharge device controllable by fluid pressure, comprising avessel, a. plurality of flexible partitions extending across said vesselto form therewith end chambers and an intermediate chamber, an anodesupported by each of said flexible partitions for movement within saidintermediate chamber and a cathode interposed between said anodes, thesaid end chambers constituting receptacles tor the fluid medium, thepressure 01' which is to control the characteristics of the spacedischarge device.

10. A space discharge device controllable by fluid pressure, comprisinga vessel, a plurality oi flexible partitions extending across saidvessel to form therewith a plurality of chambers, an anode supported byeach of said flexible partitions for movement within one of saidchambers, and a cathode interposed between said anodes, the remainingchamber constituting a receptacle for the fluid medium, the pressure 0!which is to control the characteristics of the space discharge device.

11. A space discharge device controllable by fluid pressure, comprisinga vessel, a plurality of partitions extending across said vessel andtorming therewith a plurality of chambers one oi. which is hermeticallysealed, one of said partitions being flexible, an anode supported bysaid flexible partition for movement within said hermetically sealedchamber and a cathode cooperating therewith, the remaining chamberconstituting a receptacle for the fluid medium, the pressure of which isto control the characteristics oi the space discharge device.

12. A space discharge device controllable by fluid pressure, comprisinga vessel, a plurality of partitions extending across said vessel andforming therewith a plurality of chambers, one of which is hermeticallysealed, one of said partitions being flexible, an anode and cathodeelectrode mounted. for cooperation within said hermetically sealedchamber, one of said electrodes being supported by the aforesaidflexible partition, the remaining chamber of said device constituting areceptacle for the fluid medium, the pressure of which is to control thecharacteristics oi the space discharge device.

ROSS GUNN.

